Heterogeneous network allocation vector (NAV)-based communication in wireless LAN system

ABSTRACT

In the wireless LAN system, the station STA receives a frame and updates a corresponding Inter-BSS Network Allocation Vector (NAV) or Intra-BSS NAV according to whether the frame is an Inter-BSS (Basic Service Set) frame or an Intra-BSS frame. If the received frame cannot be distinguished from the Inter-BSS frame or the Intra-BSS frame, it updates the Inter-NAV, and after receiving the frame that cannot be distinguished from the Inter-BSS frame or the Intra-BSS frame, it receives the CF-End frame, and then the corresponding NAV is reset.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2017/004220, filed on Apr. 20, 2017,which claims the benefit of U.S. Provisional Application No. 62/326,026,filed on Apr. 22, 2016, 62/342,202, filed on May 27, 2016, 62/347,117,filed on Jun. 8, 2016, 62/362,597, filed on Jul. 15, 2016, and62/364,901, filed on Jul. 21, 2016, the contents of which are all herebyincorporated by reference herein in their entireties.

TECHNICAL FIELD

The present invention relates to a wireless local area network (WLAN)system. More specifically, the present invention relates to a method andapparatus for solving the problem of operating a separate NAV (NetworkAllocation Vector) for an internal or external of BSS in a WLAN system.

BACKGROUND ART

Although a hybrid NAV communication scheme described below can beapplied to various wireless communications, a WLAN system as an exampleof applicable system to which the present invention is described.

Standards for WLAN (Wireless Local Area Network) technology have beendeveloped as Institute of Electrical and Electronics Engineers (IEEE)802.11 standards. IEEE 802.11a and b use an unlicensed band at 2.4 GHzor 5 GHz. IEEE 802.11b provides a transmission rate of 11 Mbps and IEEE802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g provides atransmission rate of 54 Mbps by applying Orthogonal Frequency DivisionMultiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmissionrate of 300 Mbps for four spatial streams by applying Multiple InputMultiple Output (MIMO)-OFDM. IEEE 802.11n supports a channel bandwidthof up to 40 MHz and, in this case, provides a transmission rate of 600Mbps.

The above-described WLAN standards have evolved into IEEE 802.11ac thatuses a bandwidth of up to 160 MHz and supports a transmission rate of upto 1 Gbit/s for 8 spatial streams and IEEE 802.11ax standards are underdiscussion.

IEEE 802.11ax system is referred to as a HE (High Efficiency) system.

DETAILED DESCRIPTION OF THE INVENTION Technical Problems

It is discussed that the HE system operates on a hybrid NAV includinginter-BSS NAV and Intra-BSS NAV. However, among the frames used in theHE system, there is the frame that is indistinguishable between theinter-BSS frame and the Intra-BSS frame. Therefore, the availableresources may not be used, or a collision may occur due to an erroneousTXOP truncation.

It is an object of the present invention to provide a method andapparatus for efficiently preventing confusion in a system using ahybrid NAV as described above.

The present invention is not limited to the technical problems describedhereinabove, and other technical problems can be derived fromembodiments of the present invention.

Technical Solutions

The object of the present invention can be achieved by providing amethod for transmitting a signal by a first station (STA) in a WirelessLocal Area Network (WLAN) system, the method comprising: receiving afirst frame, wherein an Inter-Basic Service Set (BSS) Network AllocationVector (NAV) or an Intra-BSS NAV is updated based on whether the firstframe is an Inter-BSS frame or an Intra-BSS frame, and wherein theInter-BSS NAV is updated when the first frame is indistinguishablebetween the Inter-BSS frame and the Intra-BSS frame; and receiving aContention-Free End (CF-END) frame, wherein the Inter-BSS NAV or theIntra-BSS NAV is reset in response to receiving the CF-END frame forother cases other than a first case that the CF-END frame is theInter-BSS frame and a latest NAV update is by receiving the first framedetermined as the Intra-BSS frame, and a second case that the CF-ENDframe is the Intra-BSS frame and the latest NAV update is by receivingthe first frame determined as the Inter-BSS frame; and transmitting thesignal based on the Inter-BSS NAV or the Intra-BSS NAV that have beenreset.

In another aspect of the present invention, provided herein is a firststation (STA) operating in a WLAN (wireless LAN) system, the first STAcomprising: a transceiver configured to receive a first frame and aCF-End frame; and a processor for updating an Inter-BSS NetworkAllocation Vector (NAV) or an Intra-BSS NAV based on whether the firstframe is an Inter-BSS (Basic Service Set) frame or an Intra-BSS frame,wherein the processor is configured to update the inter-BSS NAV when thefirst frame is indistinguishable between the Inter-BSS frame and theIntra-BSS frame; and when the transceiver receives the CF-END frame, theInter-BSS NAV or the Intra-BSS NAV is configured to reset based on thereception of the CF-END frame, for other cases other than a first casethat the CF-END frame is the Inter-BSS frame and a latest NAV update isby the first frame determined as the Intra-BSS frame and a second casethat the CF-END frame is an Intra-BSS frame and the latest NAV update isby the first frame determined as the Inter-BSS frame.

Preferably, the method further comprise: resetting the related Inter-BSSNAV or Intra-BSS NAV in response to receiving the CF-END frame based onwhether the latest NAV update is by receiving the first frame isindistinguishable between the Inter-BSS frame and the Intra-BSS frame.

Preferably, the method further comprise: resetting the inter-BSS NAV orthe intra-BSS NAV based on whether the CF-END frame is the Inter-BSSframe or the Intra-BSS frame.

Preferably, the method further comprise: resetting the inter-BSS NAVregardless of whether the CF-END frame is an Inter-BSS frame or anIntra-BSS frame.

Preferably, the method further comprise: setting the Inter-BSS NAV timeror the Intra-BSS NAV timer to zero at the end of the CF-END frame, whenthe Inter-BSS NAV or the Intra-BSS NAV is reset.

Preferably, wherein the first frame which is indistinguishable betweenthe Inter-BSS frame and the Intra-BSS frame, is an ACK frame or aClear-To-Send (CTS) frame.

Preferably, the method further comprise: transmitting a signal inaccordance with the Inter-BSS NAV or the Intra-BSS NAV that has beenreset, further comprising receiving a trigger frame from an access point(AP) of an Intra-BSS and transmitting an uplink data based on thetrigger frame.

Preferably, wherein the processor is further configured to reset theInter-BSS NAV or the Intra-BSS NAV based on the reception of the CF-ENDframe, when the latest NAV update is by the first frame that isindistinguishable between the Inter-BSS frame and the Intra-BSS frame.

Preferably, wherein the processor is further configured to reset theInter-BSS NAV or the Intra-BSS NAV based on whether the CF-END frame isthe Inter-BSS frame or the Intra-BSS frame.

Preferably, wherein the processor is further configured to reset theInter-BSS NAV regardless of whether the CF-END frame is the Inter-BSSframe or the Intra-BSS frame.

Preferably, wherein the processor is further configured to set anInter-BSS NAV timer or an Intra-BSS NAV timer to zero at the end of theCF-END frame, if the Inter-BSS NAV or the Intra-BSS NAV is reset.

Preferably, wherein the first frame that is indistinguishable betweenthe Inter-BSS frame and the Intra-BSS frame, is an ACK frame or aClear-To-Send (CTS) frame.

Preferably, wherein the processor is further configured to control thetransceiver to transmit an uplink data in response to the trigger framewhich is related to the Inter-BSS NAV or the Intra-BSS NAV that havebeen reset, when the transceiver receives a trigger frame from an AccessPoint (AP) of an Intra-BSS.

Advantageous Effects

As described above, while the hybrid NAV is operated through the methodand apparatus, it is possible to prevent confusion due to a framereception that cannot be distinguished from Inter-BSS frame or Intra-BSSframe.

The effects of the present invention are not limited to theabove-mentioned effects, and other advantages of the present inventionwill be more clearly understood by those skilled in the art from thefollowing description.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of a configuration of a WLAN system.

FIG. 2 illustrates another example of a configuration of a WLAN system.

FIG. 3 illustrates an exemplary configuration of a WLAN system

FIG. 4 illustrates a backoff procedure.

FIG. 5 is an explanatory diagram of a hidden node and an exposed node.

FIG. 6 is an explanatory diagram of RTS and CTS.

FIG. 7 is an explanatory diagram of a TXOP Truncation.

FIG. 8 is an explanatory diagram of a TXOP Truncation to be solved inone aspect of the present invention.

FIG. 9 is a diagram for explaining another problem in TXOP Truncation tobe solved in one aspect of the present invention.

FIG. 10 and FIG. 11 are diagrams illustrating an example of defining aTXOP Truncation scheme according to the first embodiment of the presentinvention.

FIG. 12 is a block diagram showing an exemplary configuration of an APapparatus (or base station apparatus) and a station apparatus (orterminal apparatus) according to an embodiment of the present invention.

FIG. 13 shows an exemplary structure of a processor of an AP apparatusor a station apparatus according to an embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the present invention.The following detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details. In some instances, knownstructures and devices are omitted or are shown in block diagram form,focusing on important features of the structures and devices, so as notto obscure the concept of the present invention.

FIG. 1 is a diagram illustrating an exemplary configuration of a WLANsystem.

As illustrated in FIG. 1, the WLAN system includes at least one BasicService Set (BSS). The BSS is a set of STAs that are able to communicatewith each other by successfully performing synchronization.

An STA is a logical entity including a physical layer interface betweena Medium Access Control (MAC) layer and a Physical layer of the wirelessmedium. The STA may include an AP and a non-AP STA. Among STAs, aportable terminal manipulated by a user is the non-AP STA. If a terminalis simply called an STA, the STA refers to the non-AP STA. The non-APSTA may also be referred to as a terminal, a Wireless Transmit/ReceiveUnit (WTRU), a User Equipment (UE), a Mobile Station (MS), a mobileterminal, or a mobile subscriber unit.

The AP is an entity that provides access to a Distribution System (DS)to an associated STA through a wireless medium. The AP may also bereferred to as a centralized controller, a Base Station (BS), a Node-B,a Base Transceiver System (BTS), or a site controller.

The BSS may be divided into an infrastructure BSS and an Independent BSS(IBSS).

The BSS illustrated in FIG. 1 is the IBSS. The IBSS refers to a BSS thatdoes not include an AP. Since the IBSS does not include the AP, the IBSSis not allowed to access to the DS and thus forms a self-containednetwork.

FIG. 2 is a diagram illustrating another exemplary configuration of aWLAN system.

BSSs illustrated in FIG. 2 are infrastructure BSSs. Each infrastructureBSS includes one or more STAs and one or more APs. In the infrastructureBSS, communication between non-AP STAs is basically performed via an AP.However, if a sidelink is established between the non-AP STAs, directcommunication between the non-AP STAs may be performed.

As illustrated in FIG. 2, the multiple infrastructure BSSs may beinterconnected via a DS. The BSSs interconnected via the DS are calledan Extended Service Set (ESS). STAs included in the ESS may communicatewith each other and a non-AP STA within the same ESS may move from oneBSS to another BSS while seamlessly performing communication.

The DS is a mechanism that connects a plurality of APs to one another.The DS is not necessarily a network. As long as it provides adistribution service, the DS is not limited to any specific form. Forexample, the DS may be a wireless network such as a mesh network or maybe a physical structure that connects APs to one another.

FIG. 3 illustrates an exemplary configuration of a WLAN system. In FIG.3, an exemplary infrastructure BSS including a DS is illustrated.

In the example of FIG. 3, an ESS includes BSS1 and BSS2. In the WLANsystem, an STA is a device complying with Medium Access Control/Physical(MAC/PHY) regulations of Institute of Electrical and ElectronicsEngineers (IEEE) 802.11. STAs are categorized into AP STAs and non-APSTAs. The non-AP STAs are devices handled directly by users, such aslaptop computers and mobile phones. In FIG. 3, STA1, STA3, and STA4 arenon-AP STAs, whereas STA2 and STA5 are AP STAs.

In the following description, a non-AP STA may be referred to as aterminal, a Wireless Transmit/Receive Unit (WTRU), a User Equipment(UE), a Mobile Station (MS), a Mobile Terminal (MT), or a MobileSubscriber Station (MSS). An AP corresponds to a Base Station (BS), aNode B, an evolved Node B (eNB), a Base Transceiver System (BTS), or afemto BS in other wireless communication fields.

FIG. 4 is a conceptual diagram illustrating a backoff process.

Operations based on a random backoff period will hereinafter bedescribed with reference to FIG. 4. If the occupy- or busy-state mediumis shifted to an idle state, several STAs may attempt to transmit data(or frame). As a method for implementing a minimum number of collisions,each STA selects a random backoff count, waits for a slot timecorresponding to the selected backoff count, and then attempts to startdata transmission. The random backoff count has a value of a PacketNumber (PN), and may be set to one of 0 to CW values. In this case, CWrefers to a Contention Window parameter value. Although an initial valueof the CW parameter is denoted by CWmin, the initial value may bedoubled in case of a transmission failure (for example, in the case inwhich ACK of the transmission frame is not received). If the CWparameter value is denoted by CWmax, CWmax is maintained until datatransmission is successful, and at the same time it is possible toattempt to start data transmission. If data transmission was successful,the CW parameter value is reset to CWmin. Preferably, CW, CWmin, andCWmax are set to 2n−1 (where n=0, 1, 2, . . . ).

If the random backoff process starts operation, the STA continuouslymonitors the medium while counting down the backoff slot in response tothe decided backoff count value. If the medium is monitored as theoccupied state, the countdown stops and waits for a predetermined time.If the medium is in the idle state, the remaining countdown restarts.

As shown in the example of FIG. 4, if a packet to be transmitted to MACof STA3 arrives at the STA3, the STA3 determines whether the medium isin the idle state during the DIFS, and may directly start frametransmission. In the meantime, the remaining STAs monitor whether themedium is in the busy state, and wait for a predetermined time. Duringthe predetermined time, data to be transmitted may occur in each ofSTA1, STA2, and STA5. If the medium is in the idle state, each STA waitsfor the DIFS time and then performs countdown of the backoff slot inresponse to a random backoff count value selected by each STA. Theexample of FIG. 4 shows that STA2 selects the lowest backoff count valueand STA1 selects the highest backoff count value. That is, after STA2finishes backoff counting, the residual backoff time of STA5 at a frametransmission start time is shorter than the residual backoff time ofSTA1. Each of STA1 and STA5 temporarily stops countdown while STA2occupies the medium, and waits for a predetermined time. If occupying ofthe STA2 is finished and the medium re-enters the idle state, each ofSTA1 and STA5 waits for a predetermined time DIFS, and restarts backoffcounting. That is, after the remaining backoff slot as long as theresidual backoff time is counted down, frame transmission may startoperation. Since the residual backoff time of STA5 is shorter than thatof STA1, STA5 starts frame transmission. Meanwhile, data to betransmitted may occur in STA4 while STA2 occupies the medium. In thiscase, if the medium is in the idle state, STA4 waits for the DIFS time,performs countdown in response to the random backoff count valueselected by the STA4, and then starts frame transmission. FIG. 4exemplarily shows the case in which the residual backoff time of STA5 isidentical to the random backoff count value of STA4 by chance. In thiscase, an unexpected collision may occur between STA4 and STA5. If thecollision occurs between STA4 and STA5, each of STA4 and STA5 does notreceive ACK, resulting in the occurrence of a failure in datatransmission. In this case, each of STA4 and STA5 increases the CW valuetwo times, and STA4 or STA5 may select a random backoff count value andthen perform countdown. Meanwhile, STA1 waits for a predetermined timewhile the medium is in the occupied state due to transmission of STA4and STA5. In this case, if the medium is in the idle state, STA1 waitsfor the DIFS time, and then starts frame transmission after lapse of theresidual backoff time.

STA Sensing Operation

As described above, the CSMA/CA mechanism includes not only a physicalcarrier sensing mechanism in which the AP and/or STA can directly sensethe medium, but also a virtual carrier sensing mechanism. The virtualcarrier sensing mechanism can solve some problems (such as a hidden nodeproblem) encountered in the medium access. For the virtual carriersensing, MAC of the WLAN system can utilize a Network Allocation Vector(NAV). In more detail, by means of the NAV value, the AP and/or STA,each of which currently uses the medium or has authority to use themedium, may inform another AP and/or another STA for the remaining timein which the medium is available. Accordingly, the NAV value maycorrespond to a reserved time in which the medium will be used by the APand/or STA configured to transmit the corresponding frame. A STA havingreceived the NAV value may prohibit medium access (or channel access)during the corresponding reserved time. For example, NAV may be setaccording to the value of a ‘duration’ field of the MAC header of theframe.

The robust collision detect mechanism has been proposed to reduce theprobability of such collision, and as such a detailed descriptionthereof will hereinafter be described with reference to FIGS. 5 and 6.Although an actual carrier sensing range is different from atransmission range, it is assumed that the actual carrier sensing rangeis identical to the transmission range for convenience of descriptionand better understanding of the present invention.

FIG. 5 is a conceptual diagram illustrating a hidden node and an exposednode.

FIG. 5(a) exemplarily shows the hidden node. In FIG. 5(a), STA Acommunicates with STA B, and STA C has information to be transmitted. InFIG. 5(a), STA C may determine that the medium is in the idle state whenperforming carrier sensing before transmitting data to STA B, under thecondition that STA A transmits information to STA B. Since transmissionof STA A (i.e., occupied medium) may not be detected at the location ofSTA C, it is determined that the medium is in the idle state. In thiscase, STA B simultaneously receives information of STA A and informationof STA C, resulting in the occurrence of collision. Here, STA A may beconsidered as a hidden node of STA C.

FIG. 5(b) exemplarily shows an exposed node. In FIG. 5(b), under thecondition that STA B transmits data to STA A, STA C has information tobe transmitted to STA D. If STA C performs carrier sensing, it isdetermined that the medium is occupied due to transmission of STA B.Therefore, although STA C has information to be transmitted to STA D,the medium-occupied state is sensed, such that the STA C must wait for apredetermined time (i.e., standby mode) until the medium is in the idlestate. However, since STA A is actually located out of the transmissionrange of STA C, transmission from STA C may not collide withtransmission from STA B from the viewpoint of STA A, such that STA Cunnecessarily enters the standby mode until STA B stops transmission.Here, STA C is referred to as an exposed node of STA B.

FIG. 6 is a conceptual diagram illustrating Request To Send (RTS) andClear To Send (CTS).

In order to efficiently utilize the collision avoidance mechanism underthe above-mentioned situation of FIG. 5, it is possible to use a shortsignaling packet such as RTS and CTS. RTS/CTS between two STAs may beoverheard by peripheral STA(s), such that the peripheral STA(s) mayconsider whether information is communicated between the two STAs. Forexample, if STA to be used for data transmission transmits the RTS frameto the STA having received data, the STA having received data transmitsthe CTS frame to peripheral STAs, and may inform the peripheral STAsthat the STA is going to receive data.

FIG. 6(a) exemplarily shows the method for solving problems of thehidden node. In FIG. 6(a), it is assumed that each of STA A and STA C isready to transmit data to STA B. If STA A transmits RTS to STA B, STA Btransmits CTS to each of STA A and STA C located in the vicinity of theSTA B. As a result, STA C must wait for a predetermined time until STA Aand STA B stop data transmission, such that collision is prevented fromoccurring.

FIG. 6(b) exemplarily shows the method for solving problems of theexposed node. STA C performs overhearing of RTS/CTS transmission betweenSTA A and STA B, such that STA C may determine no collision although ittransmits data to another STA (for example, STA D). That is, STA Btransmits an RTS to all peripheral STAs, and only STA A having data tobe actually transmitted can transmit a CTS. STA C receives only the RTSand does not receive the CTS of STA A, such that it can be recognizedthat STA A is located outside of the carrier sensing range of STA C.

Hybrid NAV-Based Operation

HE STA can operate a hybrid NAV such as Intra-BSS NAV as a NAV for theBSS inside, and Inter-BSS NAV as a NAV for the BSS outside. TheInter-BSS NAV among these intra-BSS NAV and inter-BSS NAV may bereferred to as a regular NAV. However, such a name may be changed (forexample, a basic NAV).

When the STA operating the 2 NAVs receives the PSDU of the intra-BSSframe, the STA can update the intra-BSS NAV according to the durationfield information of the received PSDU. In addition, when the STAreceives the PSDU of the inter-BSS frame, the STA can update the regularNAV according to the duration field information of the received PSDU.

In the above example, the corresponding NAV is updated on the basis ofthe Duration field of the received PSDU. However, Intra-BSS NAV orRegular NAV may be equally updated through the TXOP Duration of the HESIG-A of the received HE PPDU.

If the RA field of the received frame indicates the STA itself, the STAwill not update the corresponding NAV. However, if the RA field of thereceived frame does not indicate the STA itself, the corresponding NAVcan be updated based on information of the Duration field of the PSDU orthe TXOP Duration field of the HE SIG-A, based on whether the receivedframe is an Inter-BSS frame or an Intra-BSS frame.

Thus, if two NAVs are supported by a particular STA, one or more ofthese NAVs are considered and one or more NAV counters are not zero, thevirtual CS may determine that the medium is Busy.

Truncation of TXOP

In one aspect of the present invention, it is intended to solve theconfusion in the TXOP truncation problem in the STA using two NAVs asdescribed above. The concept of TXOP Truncation is explained here.

FIG. 7 is an explanatory diagram of a TXOP Truncation in an aspect ofthe present invention.

If the STA acquires the access right (TXOP) for the channel using theEDCA and there are enough remaining segments to transmit all of itsdata, the corresponding STA can transmit the CF-END frame.

Accordingly, the receiving STA that has received the CF-END frame resetsthe NAV, and specifically, can set the NAV timer to 0 at the end of thisframe.

FIG. 7 shows an example in which TXOP truncation is performed based onthis principle. First, the STA is connected to the channel using theEDCA channel connection and then the STA can transmit a nay-set sequence(e.g., RTS/CTS). Thereafter, after SIFS, the STA may send aninitiator-sequence that may include multiple PPDU exchanges.

If STA doesn't have more data to transmit, the STA as a TXOP holder, canperform a TXOP Truncation by transmitting a CF-END frame, and thereceiving side can also reset the NAV.

As described above, in the case of an STA that operates two NAVs, it isassumed in the embodiment of the present invention that two NAVs areindependently operated to perform a TXOP Truncation as follows.

First, when the STA receives the CF-END frame in the inter-BSS, the STAcan perform the TXOP Truncation by resetting the regular NAV. Also, whenthe STA receives the CG-END frame of the Intra-BSS, the intra-BSS NAVcan be reset, and the TXOP Truncation can be performed.

Problems with a Frame that Cannot Distinguish a BSS

Hereinafter, the problem of TXOP Truncation will be described in detailwhen a STA using two NAVs receives frame that cannot distinguish BSS.

In general, the STA can identify the frame is an Inter-BSS frame or anIntra-BSS frame with the BSSID of the address information (RA or TAinformation) included in the BSS Color of the HE-SIG A in the HE PPDU orMAC header.

However, when the STA receives a frame (for example, ACK or CTS) thatcannot distinguish the BSS, it could be a problem how to handle it.

According to an embodiment of the present invention, when the STAreceives a frame that cannot distinguish between an Inter-BSS frame andan Intra-BSS frame, it is assumed that the frame is set to update theregular NAV if the frame wasn't transmitted to the STA.

However, when it is simply updating the Regular NAV in this way, thefollowing problems may occur.

FIG. 8 is a diagram for explaining a problem in TXOP Truncation to besolved in one aspect of the present invention.

In the example of FIG. 8, it is assumed that the intra-BSS AP transmitsa CTS frame to the STA (S810). Since the CTS frame cannot bedistinguished between the inter-BSS frame and the Intra-BSS frame by thereceiving STA, the STA updates only the regular NAV and does not updatethe intra-BSS NAV according to the above assumption.

Thereafter, if the CF-End frame is received in the Intra-BSS (S820), theRegular NAV is not truncated.

Accordingly, even when a Trigger Frame for the data transmission isreceived from the AP of the Intra-BSS (S830), the STA cannot transmitthe UL MU frame.

FIG. 9 is a diagram for explaining another problem in TXOP Truncation tobe solved in one aspect of the present invention.

In FIG. 9, it is assumed that the intra-BSS AP transmits a CTS frame tothe STA (S910). Since the CTS frame cannot be distinguished from theinter-BSS frame or the Intra-BSS frame by the receiving STA, the STAupdates only the regular NAV and does not update the intra-BSS NAVaccording to the above assumption.

Then, it is assumed that a CF-END frame is received from the AP of theInter-BSS in FIG. 9 (S920). In this case, since the NAV which is set bythe CTS frame transmitted from the Intra-BSS AP, is a Regular NAV, theRegular NAV is reset because the corresponding CF-END frame is received,and then the STA can transmit the frame (S930). In this case, if theHidden STA of the Intra BSS is transmitting to the AP, there may be aproblem in the reception of the AP.

To solve such the above problems, various embodiments are presented.

Embodiment 1—Case 1, if it is Difficult to Identify the Inter/Intra BSSand the Condition Updating the Regular NAV is Maintained

In this embodiment, the above-described problem is solved under theassumption that the condition that the regular NAV is updated by thereceived frame that cannot be distinguished from Intra-BSS or Inter-BSSis maintained.

FIG. 10 and FIG. 11 are diagrams illustrating an example of defining aTXOP Truncation scheme according to the first embodiment of the presentinvention.

In FIG. 10, when the regular NAV is updated by the received frame thatcannot be distinguished from the Intra-BSS or Inter-BSS (S1010), and theCF-End frame is received from the Intra-BSS STA (S1020), it is proposedto reset only the Intra-BSS NAV without resetting (/truncation) theRegular NAV. Because the Intra-BSS NAV is reset as described above,after that, when a trigger frame is received from the AP of theIntra-BSS (S1030), the UL MU frame can be transmitted (The problem ofFIG. 8 is solved).

FIG. 11, when the regular NAV is updated by the received frame thatcannot be distinguished from the Intra-BSS or Inter-BSS (S1110), and theCF-End frame is received from the Inter-BSS STA (S1120), it is suggestedthat the regular NAV is not reset (/truncated). Accordingly, even if theUL MU resource is allocated by the trigger frame of the Intra-BSS AP asshown in FIG. 11, it doesn't get a response of transmitting the UL MUframe. (The problem of FIG. 9 is solved).

Embodiment 2—Case 2, if it is Difficult to Identify the Inter/Intra BSSand the Condition Updating the Regular NAV is Maintained

In this embodiment, the above-described problem is solved under theassumption that the condition that the regular NAV is updated by thereceived frame that cannot be distinguished from Intra-BSS or Inter-BSSis maintained.

In this embodiment, when the regular NAV is updated by the receivedframe that is indistinguishable between the Intra-BSS and Inter-BSS, thefollowing performance is proposed. That is, if the CF-End frame isreceived from the Inter-BSS STA, the regular NAV is reset (truncated),and if the CF-End frame is received from the Intra-BSS STA, theIntra-BSS NAV and the regular NAV is reset (/truncate)

Also, if the regular NAV is updated by the received frame that isindistinguishable between the Intra-BSS and Inter-BSS, the UL MUresource is allocated by the trigger frame of the intra-BSS AP, theIntra-BSS NAV and the Regular NAV is not considered. That is, since thetwo NAVs are not considered, if the physical carrier sensing is idle,the UL MU frame can be transmitted to the allocated area.

Embodiment 3—Case 3, if it is Difficult to Identify the Inter/Intra BSSand the Condition Updating the Regular NAV is Maintained

In the present embodiment, when the following conditions are satisfied,it is set that NAV is not reset in response to the CF-END framereception.

(1) If the received CF-END frame is the inter-BSS frame and the latestNAV update is performed by the intra-BSS frame, and

(2) The received CF-END frame is the intra-BSS frame, and the latest NAVupdate is performed by the inter-BSS frame.

It is also proposed to set the NAV of the STA to be reset in the casesother than the cases (1) and (2) above.

That is, in this embodiment, when the frame that cannot be distinguishedfrom the Inter-BSS frame or the Intra-BSS frame is received as describedabove, the Regular NAV is updated. After that, if the CF-END frame isreceived, it is regarded as the corresponding NAV reset, and the NAVtimer can be set to 0 at the end of the PPDU including the frame. Thatis, if it is not a condition that the NAV reset is not performed as inthe above (1)-(2), the NAV may reset, regardless of whether the CF-ENDframe is the Inter-BSS frame or Intra-BSS frame.

At this time, it can be decided whether the Intra-BSS NAV is updated orthe regular NAV is updated in accordance whether the CF-END frame is theInter-BSS frame or Intra-BSS frame

In addition, in an embodiment of the present invention, the regular NAVcan be reset regardless of whether the CF-END frame is an Inter-BSSframe or an Intra-BSS frame.

According to the embodiment, when the CF-END frame is received from theAP of the Intra-BSS in step S820 in the case shown in FIG. 8, since theconditions of (1) and (2) are not satisfied, the STA reset the NAV, andthen the problem described in FIG. 8 can be solved.

Embodiment 4—Case 1, if it is Difficult to Identify the Inter/Intra BSSand the Condition Updating the Regular NAV is Changed

In this embodiment, when an STA supporting Two NAVs receives a frame(e.g., CTS or ACK) that cannot be distinguished from Intra-BSS orInter-BSS, instead of updating the Regular NAV for NAV concerning theInter-BSS, it is proposed to update the Intra-BSS NAV. In this case,Intra-BSS NAV can be called Regular NAV.

That is, the STA updates the Intra-BSS NAV by the frame (e.g., CTS orACK) that cannot be distinguished from Intra-BSS or Inter-BSS.

If the frame is transmitted by the Intra-BSS STA and the Inter-BSSCF-End frame is received, since the Intra-BSS NAV is not reset, theproblem situation shown in FIG. 8 does not occur (Case 1).

If the frame is transmitted by the Intra-BSS STA and the STA isallocated the UL resource by the transmission of the trigger frame ofthe Intra-BSS AP, since the Intra-BSS NAV is set, the problem situationmentioned in FIG. 9 does not occur (Case 2).

If the frame is transmitted by the Intra-BSS STA and the Intra-BSSCF-End frame is received, the STA immediately resets the Intra-BSS NAV(Case 3).

If the frame is transmitted by the Inter-BSS STA and the Inter-BSSCF-End frame is received, since the Intra-BSS NAV is not reset, the STAcan occur the over-protection by maintaining the Intra-BSS NAV (Case 4).

If the frame is transmitted by the inter-BSS STA and the STA isallocated the UL resource by the transmission of the trigger frame ofthe intra-BSS AP, the STA can transmit the UL frame because theintra-BSS NAV is established. In this case, it may affect thetransmission of the Inter-BSS STA (Case 5).

If the frame is transmitted by the Inter-BSS STA and the Intra-BSSCF-End frame is received, since the STA may reset the Intra-BSS NAV andit may affect the transmission of the Inter-BSS STA (Case 6).

The influence to the transmission of the inter-BSS STA of the case 5 andthe case 6 was also a problem in the conventional method (operation withone NAV) and it is not a problem because the influence can be preventedby the position of the receiver. However, when the existing method isused, it is important to be always able to influence to it's BSS or notto transmit the UL MU frame.

Embodiment 5—Case 2, if it is Difficult to Identify the Inter/Intra BSSand the Condition Updating the Regular NAV is Changed

In this embodiment, when a frame that cannot be distinguished fromIntra-BSS or Inter-BSS is received, it is proposed to additionallymaintain NAV for the frame. That is, the STA maintains three NAVs.

NAV1 maintains and manages the Intra-BSS NAV, NAV2 maintains and managesthe Inter-BSS NAV, and the NAV3 maintains and manages other NAV. OtherNAV (NAV3) is updated when it receives a frame that areindistinguishable from Inter-BSS or Intra-BSS. If the NAV3 is not 0, itcannot transmit a frame. The NAV3 is not truncated by the CF-END.

FIG. 12 is a block diagram showing an exemplary configuration of an APapparatus (or base station apparatus) and a station apparatus (orterminal apparatus) according to an embodiment of the present invention.

The AP 100 may include a processor 110, a memory 120, and a transceiver130. The station 150 may include a processor 160, a memory 170, and atransceiver 180.

The transceivers 130 and 180 may transmit/receive a wireless signal andmay implement, for example, a physical layer according to the IEEE 802system. Processors 110 and 160 may be coupled to transceivers 130 and180 to implement a physical layer and/or a MAC layer according to theIEEE 802 system. Processors 110 and 160 may be configured to perform anoperation in accordance with one or more combinations of the variousembodiments of the invention described above.

In addition, a module implementing the operations of the AP and thestation according to various embodiments of the present inventiondescribed above may be stored in the memories 120 and 170 and executedby the processors 110 and 160. The memories 120 and 170 may be includedin the internal of the processors 110 and 160 or may be installed in theexternal of the processors 110 and 160 and connected by the processors110 and 160 and known means.

The description of the above-described AP apparatus 100 and stationapparatus 150 can be applied to the base station apparatuses andterminal apparatuses in other wireless communication systems (forexample, LTE/LTE-A system), respectively

The specific configurations of the AP and the station apparatus may beimplemented such that the elements described in the various embodimentsof the present invention described above may be applied independently ortwo or more embodiments may be applied at the same time. For the sake ofclarity, the redundant description is omitted.

FIG. 13 shows an exemplary structure of a processor of an AP apparatusor a station apparatus according to an embodiment of the presentinvention.

The AP or the processor of the station may have a plurality of layersand FIG. 13 shows a detailed structure in which a MAC sublayer 3810 anda physical layer 3820 on a DLL (Data Link Layer). As shown in FIG. 13,the PHY 3820 may include a Physical Layer Convergence Procedure (PLCP)entity 3821 and a PMD (Physical Medium Dependent) entity 3822. Both theMAC sublayer 3810 and the PHY 3820 conceptually include managemententities called MLME (MAC sublayer Management Entity) 3811,respectively. These entities 3811 and 3821 provide a hierarchicalmanagement service interface in which hierarchical management functionsoperate.

To provide correct MAC operation, a Station Management Entity (SME) 3830exists within each station. SME 3830 is a layer-independent entity thatmay be present in a separate management plane or may seem to beoff-the-side. Although precise functions of SME 3830 are notspecifically described in this document, generally, such an entity 3830may appear to be responsible for collecting layer-dependent states fromvarious Layer Management Entities (LMEs), similarly setting the valuesof layer-specific parameters, and so on. The SME 3830 typically performsthese functions on behalf of the generic system management entity andcan implement standard management protocols.

The entities shown in FIG. 13 interact in various ways. FIG. 13 showssome examples of exchanging GET/SET primitives. The XX-GET.requestprimitive is used to request the value of a given MIB attribute. TheXX-GET.confirm primitive returns the appropriate MIB attributeinformation value if the Status is “Success”, otherwise it is used toreturn an error instruction in the Status field. The XX-SET.requestprimitive is used to request that the indicated MIB attribute is set tothe given value. When the MIB attribute indicates a specific operation,it is requested that the corresponding operation is performed. TheXX-SET.confirm primitive confirms that the indicated MIB attribute isset to the requested value if the status is “successful”, otherwise itis used to return an error condition to the status field. If the MIBattribute indicates a specific action, this confirms that the action hasbeen performed.

As shown in FIG. 13, MLME 3811 and SME 3830 may exchange variousMLME_GET/SET primitives through MLME_SAP 3850. Also, the variousPLCM_GET/SET primitives can be exchanged between the PLME 3821 and theSME 3830 via the PLME_SAP 3860 and the MLME 3811 and the PLME 3870 viathe MLME-PLME_SAP 3870.

The above-described embodiments of the present invention can beimplemented by various means. For example, embodiments of the presentinvention may be implemented by a hardware, firmware, software, or acombination thereof.

In the case of hardware implementation, the method according toembodiments of the present invention may be implemented in one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), FPGAs (Field Programmable GateArrays), processors, controllers, microcontrollers, microprocessors, andthe like.

In the case of an implementation by a firmware or software, the methodaccording to embodiments of the present invention may be implemented inthe form of a module, a procedure or a function for performing thefunctions or operations described above. The software code may be storedin a memory unit and driven by the processor. The memory unit may belocated inside or outside the processor, and may exchange data with theprocessor by various well-known means.

The detailed description of the preferred examples of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the preferred examples, those skilled in the art willappreciate that various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention described in the appended claims. Accordingly, the inventionshould not be limited to the specific examples described herein, butshould be accorded the broadest scope consistent with the principles andnovel features disclosed herein.

INDUSTRIAL APPLICABILITY

As described above, the embodiments of the present invention can beapplied to various wireless communication systems including an IEEE802.11 system.

The invention claimed is:
 1. A method for transmitting a signal by a first station (STA) in a Wireless Local Area Network (WLAN) system, the method comprising: receiving a first frame; updating an Intra-Basic Service Set (BSS) Network Allocation Vector (NAV) based on the first frame being an Intra-BSS frame; updating an Inter-BSS NAV based on the first frame being an Inter-BSS frame or the first frame being indistinguishable between the Inter-BSS frame and the Intra-BSS frame; and receiving a Contention Free (CF)-END frame, resetting both of the Inter-BSS NAV and the Intra-BSS NAV based on that the CF-END frame is the Intra-BSS frame and the inter-BSS NAV was updated due to the first frame being indistinguishable between the Inter-BSS frame and the Intra-BSS frame; and transmitting the signal based on the Inter-BSS NAV or the Intra-BSS NAV that have been reset.
 2. The method of claim 1, further comprising resetting the Inter-BSS NAV based on that the CF-END frame is the Inter-BSS frame.
 3. The method of claim 1, further comprising setting the Inter-BSS NAV timer or the Intra-BSS NAV timer to zero at the end of a Physical Protocol Data Unit (PPDU) including the CF-END frame, to reset the Inter-BSS NAV or the Intra-BSS NAV.
 4. The method of claim 1, wherein the first frame which is indistinguishable between the Inter-BSS frame and the Intra-BSS frame, is an ACK frame or a Clear-To-Send (CTS) frame.
 5. The method of claim 1, wherein transmitting the signal in accordance with the Inter-BSS NAV or the Intra-BSS NAV that has been reset, further comprises receiving a trigger frame from an access point (AP) of an Intra-BSS and transmitting an uplink data based on the trigger frame.
 6. A first station (STA) operating in a WLAN(wireless LAN) system, the first STA comprising: a transceiver configured to receive a first frame and a Contention Free (CF)-End frame; and a processor for updating an Inter-BSS Network Allocation Vector (NAV) or an Intra-BSS NAV based on whether the first frame is an Inter-BSS (Basic Service Set) frame or an Intra-BSS frame, wherein the processor is configured to update the inter-BSS NAV when the first frame is indistinguishable between the Inter-BSS frame and the Intra-BSS frame; and wherein the processor is configured to reset both of the Inter-BSS NAV and the Intra-BSS NAV based on that the CF-END frame is the Intra-BSS frame and the inter-BSS NAV was updated due to the first frame being indistinguishable between the Inter-BSS frame and the Intra-BSS frame.
 7. The first station (STA) of claim 6, wherein the processor is further configured to reset the Inter-BSS NAV based on that the CF-END frame is the Inter-BSS frame.
 8. The first station (STA) of claim 6, wherein the processor is further configured to set an Inter-BSS NAV timer or an Intra-BSS NAV timer to zero at the end of a Physical Protocol Data Unit (PPDU) including the CF-END frame, to reset the Inter-BSS NAV or the Intra-BSS NAV.
 9. The first station (STA) of claim 6, wherein the first frame that is indistinguishable between the Inter-BSS frame and the Intra-BSS frame, is an ACK frame or a Clear-To-Send(CTS) frame.
 10. The first station (STA) of claim 6, wherein the processor is further configured to control the transceiver to transmit an uplink data in response to a trigger frame which is related to the Inter-BSS NAV or the Intra-BSS NAV that have been reset, when the transceiver receives the trigger frame from an Access Point (AP) of an Intra-BSS. 